Vehicle traffic control system

ABSTRACT

A vehicle traffic control system has been provided having communication means including a pair of line wires and remotely located control apparatus for transmitting control signals to and receiving traffic information from, a local controller over said communications means. The controller operates to provide signals for controlling vehicle traffic in accordance with control signals and also operates to provide signals for controlling the vehicle traffic independently when remote control is terminated. The improvement for communicating controls between the remotely located controller and at least two control devices coupled to said remote controller includes means at the control point for selectively designating a control frequency and auxiliary means coupled to the local station control devices responsive to the initiation of said control frequency for selectively energizing one or the other of said control devices in accordance with the duration of the control frequency.

United States Patent [151 3,651,453

Bolton et al. [4 1 Mar. .21, 1972 [54] VEHICLE TRAFFIC CONTROL SYSTEM [57] I ABSTRACT [72] Inventors: Norman A. Bolton, Scottsville; Klaus H. A vehicle traffic control system has been provided having Frlellnghaus, R ch ster, th of NY communication means including a pair of line wires and remotely located control apparatus for transmitting control [73] Asslgnee' g signal Corporation Rochester signals to and receiving traffic information from, a local controller over said communications means. The controller Filed! 12, 1970 operates to provide signals for controlling vehicle traffic in ac- [21] APPI No; 18,979 cordance with control signals and also operates to provide signals for controlling the vehicle traffic independently when remote control is terminated. The improvement for commu- US. Cl. "340/42, A nicating controls between the remotely located controller and 1 lllt. Cl. G08! t l t t t l d i l d t id remote controller [581 Field of Search "340/42, 171 171 includes means at the control point for selectively designating 340/147 167 A a control frequency and auxiliary means coupled to the local station control devices responsive to the initiation of said con- [56] References Cited I trol frequency for selectively energizing one or the other of UNITED STATES PATENTS said control devices in accordance with the duration of the control frequency. 2,001,440 5/1935 West ..340/42 2,515,968 7/1950 Shanklin ..340/l67 A Primary Examiner-Ralph D. Blakeslee 11 Claims, 2 Drawing Figures Attorney-Harold S. Wynn so s! l8 R L R F W I 1 R 49 47- R0 F0 H; I)? lfhn I 67 I I I l z: V I

F I I cl I L 1 Fl I F I I I I --l C I I L l =l= I I C L T..! I OI I LL I LL I u v1 l A I 0 0 i. I l I I I R, R. I I I I I I I I I I CONTROL 63 I I I SHIFT H I I 45 I I I STEP a I STAND BY I I I DA I X I I I GREE N 0 INFO t I I COMPUTER @103; a I w; I

VEHICLE TRAFFIC CONTROL SYSTEM BACKGROUND OF THE INVENTION The invention relates to vehicle traffic control systems and in particular to means for controlling a number of remotely located control devices operable for providing indications to vehicle trafiic for a more efficient control of the flow of the trafiic.

In modern vehicle traffic control systems, it is desirable to control the signals at a number of intersections by using a computer coupled to field-located apparatus. The local controller responsive to control signals from the computer actuates the appropriate traffic signals. Each local controller generally has a mechanical or electronic stepping device which periodically moves through a cycle of operations for controlling each of the various signals at the intersection. These signals may be, for example, stop, caution, go, pedestrian walk, or dont walk and left turn or right turn signals and the like. Generally, the communications link between the computer and the local controller is one or more dedicated pairs of telephone transmission lines. In order to efficiently control the signals at the intersection, it is desirable to maximize the amount of information being transmitted over the line wires so that generally only one pair of telephone lines is necessary for controlling each intersection effectively. In order to further reduce the cost per intersection, low frequency signals are used out of the human voice range so that advantage may be taken of lower leasing rates for the telegraphtype lines. The use of low frequency signals and the physical constraints of the transmission lines as, for example, the distributed capacitance, inductance and resistance of those lines provide problems which have heretofore been difficult to alleviate. In addition, maximizing the amount of information transmitted back and forth between the computer and each intersection requires certain novel additions to the circuitry which shall hereinafter be described.

It is therefore an object of the present invention to provide an arrangement which substantially obviates the limitations and disadvantages of the described prior art arrangements.

It is another object of the invention to provide for control of a number of auxiliary devices which may be necessary to control traffic more efficiently at the particular intersection.

SUMMARY OF INVENTION A vehicle traffic control system has been provided having communication means including a pair of line wires and remotely located control apparatus for transmitting control signals to and receiving traffic information from, a local controller over said communication means. The local controller is operable to provide signals for controlling the vehicle traffic in accordance with the control signals and also is operable to provide signals for controlling the vehicle traffic independently when remote control is terminated. The improvement for communicating controls between the remotely located controller and at least two control devices coupled to said controller includes means at the control point for selectively designating a control frequency and auxiliary means coupled to the local station control devices responsive to the initiation of the control frequency for selectively energizing one or the other of said control devices in accordance with the duration of the control frequency. A system also is provided to communicate a cancel control signal from the ofiice to the local control devices for shifting the devices from remote control.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description, taken in connection with the accompanying drawings, while the scope will be pointed out in the appended claims.

FIG. 1A is the interface circuitry coupled between the central computer and the transmission lines which are also included in the drawing.

FIG. 1B is an interface coupled between the transmission lines and the various devices to be controller by the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The elements in FIGS. 1A and 1B are in their normal state and any changes shall be hereinafter described in order to explain their various functions. Accordingly, controls A and B in FIG. 1B are in a deenergized state and activation of the auxiliary controls is accomplished through the use of time dependent signals from the ofiice according to the concepts of the present invention.

The office and field stations are connected over lines wires L, l at terminals 0, O and F, F, respectively. Nonnally, l0 hertz square wave signals pole changed alternately and about a common ground are transmitted over a back contact 11 of control shift relay 10 through output resistor R, and fuse F to terminal 0 over line wire L including the distributed resistance R and inductance L, to terminal F and through fuse F and input resistor R through zener diodes 12 and 13, resistors 14 and 15, diode 16 and computer online relay 17 thence to input resistor R fuse F and back to the office over line wire L through distributed inductance and resistance R and L through fuse F output resistor R diode 50, resistor 49, closed front contact 46 of relay 45, back contact 19 of relay 10 to the other side of the ten hertz signal. Resistor l8 permits a very small current to flow when contact 46 is open in order that the 15 hertz detector can function during this time. Computer online relay 17 is only activated for onehalf cycle of each 10 hertz signal because diode 16 only permits a positive half-cycle to pass through relay coil 17 so that contact 22 of relay 17 is closed only for each positive halfcycle of the 10 hertz signal. However, computer online relay repeater 23 remains normally energized because of the slugging provided by capacitor 24 and resistor 25.

In order to energize control A, the following sequence of events must occur. Control shift relay 10 is energized shifting contacts 1 1 and 19 to 15 hertz terminals of the input. As previously described, the computer online relay 17 and its repeater relay 23 remain pulsing and energized respectively. However, the 15 hertz signal is coupled to the 15 hertz detector 26 via the tap between the junction of resistors 14 and 15 through diac 27, inductor 28 to the primary of the transformer 29. The 15 cycle signal activates the detector 26 and an output signal is provided to control shift relay 30. When relay 30 is energized, capacitor 31 is charged from energy through resistor 31 and front contact 32. Biasing resistor 34 maintains timer 35 in a deenergized condition when relay 30 is deenergized. Positive energy through front contact 33 initiates a timeout cycle in timer 35. Capacitor 31 is sufficiently charged within a half of second and the timeout cycle of timer 35 is sufficiently long so that no output is produced for energizing long shift relay 56. If relay 30 is energized for approximately one-half second and then subsequently deenergized, energy in charged capacitor 31 is transmitted through back contact 32 and back contact 37 of relay 56 and back contact 38 for energizing polar relay 40-40 to a forward condition which shifts contact 41 from the back to the forward position energizing auxiliary control A. If, on the other hand, it is desired to energize control B, the control shift relay 30 must be energized for greater than the timeout cycle of timer 35. This is accomplished by maintaining the 15 hertz signal on the input at the office. The 15 hertz signal is detected and contact 33 of relay 30 is held in the forward position long enough so that timer 35 can complete its timeout cycle and produce an output for energizing long shift relay 56. When this relay is energized and relay 30 is deenergized the energy is transmitted from the charged capacitor 31 again through back contact 32 to the front contact 37 of relay 56 which provides energy to back contact 42 of polarized relay 39-39 and thence to energize to a forward condition polarized relay 43-43. With relay 43-43 energized, the contact 44 is shifted to its forward'position thus energizing auxiliary control B. From the drawing it can be seen that the polarized relays 40-40 and 43-43 remain in their last energized position thus providing a memory to the auxiliary control A and B. Unless the shift to the 15 cycle signal is provided under the correct condition, controls A and B remain in their last energized position.

In order to energize either of the controls A and B to the reverse condition, the shift to 15 hertz must be accomplished within a certain period of time after the controller is stepped by the computer. This stepping of the controller is provided because generally an electronic circuit or a motor is energized by a stepping relay. Each step of the relay moves the electronic circuitry or the motor to the next position to which it has been programmed. Stepping of the controller is necessary in order that the circuitry in the field indicated by the legend step controller may be activated each time the office apparatus is stepped. The circuitry in the field responds to these signals for activating either an electronic counter circuit or an electric motor having a cam with contact points thereon for activating certain circuits which energize the light signals at the intersection. The controller in the field may be stepped by the deenergization of a relay at the office end which subsequently deenergizes a repeater relay in the field which provides a signal to step the controller. This is accomplished by the computer by removing a signal to step and standby relay 45 which deenergizes the relay and opens front contact 46. The opening of contact 46 adds impedance to a parallel circuit including resistor 18, diode 50, resistor 49, resistor 47 and capacitor 48. The circuit described for energizing or maintaining the pulsing of computer online relay 17 is thus changed by the additional impedance and the relay 17 becomes deenergized, and computer online repeater relay 23 is subsequently deenergized closing back contact 50 which couples positive energy to the stepper controller terminal. The deenergization of computer online repeater relay 23 also closes back contacts of contactors 51 and 52. Such a condition will have no effect on controller A and B nor on timer 53 unless this deenergization is maintained for the cycle time of timer 53. Once timer 53 is activated by the removal of the common from contact 52, it times out in approximately 3 seconds. If repeater relay 23 is maintained off for this amount of time, a signal produced by timer 53 deenergizes the off standby relay 54 which in turn drops contacts 55 and 56. Once these relays are deenergized, the controller at the field end of the system shifts off standby to an activated state and circuitry associated therewith maintains the operation of the intersection lights even though the computer has relinquished control of the field station. This may occur, for example, if a short circuit occurs on the line or a malfunction occurs at the computer, then in order that the intersection control is maintained, the controller at the intersection can provide the signals necessary for maintaining traffic flow. in addition to this factor, the deenergization of relay 23 also provides energy to relay 39-39. This is accomplished through a charged capacitor 57. The energy provided by the capacitor 57 picks relay 39 and its contactor 39A which starts a timing cycle in timer 59. The timing cycle of timer 59 is somewhat less than the timing cycle of timer 53. Then after approximately 2 seconds, the timer provides a signal to relay 39 and again energizes that relay to its reverse condition and also its associated contacts.

In order to cancel a signal at A or B, it is therefore necessary to step the controller and within the timeout cycle of timer 59, shift to the control shift frequency so that when relays 39-39 are energized forward, their associated contacts 38 and 42 will be in the front position and cause their respective relays 40 and 43 to be energized to the reverse or back contact position and contactors 41 and 44 respectively will cancel the control to the associated A or B relay. This, however, assumes again that the long shift relay has been energized or deenergized to its appropriate position as previously described.

The resistor 60-capacitor 61 combination in FIG. 1A is provided to suppress the arc when contact 19 and 11 are open during a portion of the cycle when voltage is applied to the and hertz inputs.

it is necessary for the computer to be advised of the position of the signals at the intersection. The phase A green signal is useful for providing this information. Each time the controller steps through a cycle it will energize the green light signal at the intersection and energy from this signal is provided to fullwave rectifier including diodes 62. Energy from the green signal activates relay 63 which in turn closes front contact 64. The closing of contact 64 allows current flow during the positive half-cycle which permits an energization of the office operated relay 67 on the positive half-cycle. It should be noted that R65 and C66 is a contact suppression network. Resistor 95 allows a small current to flow when contact 64 is open so that the 15 hertz detector can operate during this time. The input signal provides energy directly to relay 67 energizing it and picking front contact 69. On the negative half-cycle, energy is passed out of the office and over the lines into the field circuitry through wire 20, fuse F resistor R, and zener diodes l2 and 13, through diode l6, relay l7, resistor R, and fuse F over the line back through fuse F and resistor R through diode 50, resistor 49, contact 46, if it is closed, and back to the energy source by way of contact 19. 1f contact 46 is open, current at office end passes through resistor 18 instead of through diode 50, resistor 49 and contact 46. During this same negative half-cycle, current flows from the common terminal CT, through upper relay coil 68, diode 74, resistor 73, closed contact 69, through lower relay coil 67 and back to the energy source by way of contact 19. This particular current flow picks up relay 68 and sticks up relay 67. When the positive halfcycle returns, the current flow that was described for the previous positive half-cycle is again established. At the same time, current also flows through resistor 81, diode 82, through now closed contact 75 through the lower coil of relay 68. This current flow sticks relay 68 in its energized position during the positive half-cycle of line signal. The energization of relay 68 closes contact which provides the phase green information to the computer and basically repeats the operation of the phase A green relay 63 in the field.

When the controller in the field steps out of the phase A green aspect, relay 63 becomes deenergized, opening contact 64. On the next positive half-cycle of the line signal, current ceases to flow through the upper coil of relay 67 because contact 64 is open. This causes relay 67 to drop, opening contact 69. Note relay 68 still remains energized by current flow through its lower coil stick circuit. On the negative half-cycle relay 68 drops because relay pick current through the upper coil of relay 68 is cut off due to the open contact 69.

The reason for the two relays 67 and 68 circuit to detect the operation of the phase A green relay 63 is because of the interline capacitance C between the line wires of a medium to long line. When the interline capacitance C, is sufficiently large and the line is in its positive half-cycle, a current pulse will flow through the upper coil of relay 67 even though contact 64 is open. This current flow is a transient current flow that flows through the upper coil of relay 67, through diode 71, resistor R fuse F and charges the line capacitance C This current is sufficiently great to cause relay 67 to pick up. Once the line capacitance C is charged up, this transient current flow decreases to zero and relay 67 again drops if it is not yet the end of the positive half-cycle of the line signal. Therefore, when the line changes to its negative half-cycle, relay 68 cannot be energized because contact 69 is again open. Resistor 72 provides a small amount knockdown bias during the positive half-cycle to insure that relay 67 drops because the end of the positive half-cycle when contact 64 is open and relay 67 initially is energized by the line capacitance charging current. Note relay 68 can only pick up if relay 67 is still energized, closing contact 69 at the end of the positive half-cycle. This condition will only exist if contact 64 is closed. Thus the double relay circuit provides discrimination against line charging currents from falsely closing the office A phase green contact 80. Note capacitor 78, resistor 77, capacitor 66 and resistor 65 are contact protection networks for contacts 69 and 64.

Because of the low frequency requirements of this type of a transmission line, the distributed capacitance, resistance and inductance of the transmission line is an important factor in the determination of the ofiice and field equipment circuitry. Distributed resistances R and inductances L,, as well as the distributed capacitance across the line C and distributed capacitance to ground C attenuate the signals transmitted between the office and the field immensely. It is for this reason that various repeater circuits and stick circuits are necessary for maintaining and deenergizing the appropriate relays at the proper times. The circuitry of the present invention is operable over varying distances, for example, from a few hundred feet to 15 miles. However, the circuitry involved may be less complicated if the distributed capacitance is low by virtue of the field station being close to the office control point.

The 15 hertz detector as employed in the present invention is a unique filtering device utilizing gating techniques to discriminate between the and hertz signals. The physical construction of transformer 29 includes a square loop core 29A which becomes saturated after each pole change of the 10 or 15 hertz signal. That is, it acts as a permanent magnet aligned in accordance with the polarity of the input signal and pulses having the same polarity have virtually no effect at the secondary side of the transformer 29 which is input to detector 26. When the signals to the primary are pole-changed, the core 29A becomes saturated in the opposite polarity and produces a strong secondary signal and again virtually isolates the detector 26 from the primary of the transformer 29 for subsequent pulses of the same polarity.

Resistors 14, 15 and capacitor 15A block the sharp short noise pulses that might be present on the line from effecting the proper operation of detector 26. In normal operation when the line signal has changed polarity, capacitor 15A charges up through resistor 14. The two back to back zener diodes l2 and 13 provide a constant charging voltage in either line signal polarity regardless of line load or line length. The diac 27 is a three layer diode which has an equal voltage breakdown threshold in either polarity. Therefore, until capacitor 15A has charged up to the breakdown threshold of diac 27, this diode blocks current from flowing through inductor 28 and the primary of transformer 29. When this capacitor 15A has charged up to the diode breakdown threshold, diac 27 breaks down abruptly and capacitor 15A is suddenly discharged through inductor 28 and the primary of transformer 29. If this is the first pulse of this polarity, the core of transformer 28 is suddenly switched from its previous remnant state to its new opposite state and an output pulse is generated in the secondary windings. Once capacitor 15A is discharged, diac 27 again blocks the current flow and the capacitor 15A is again charged up. At the threshold, diac 27 again breaks down and suddenly discharges the capacitor charge through the primary of transformer 29. Since it is in the same direction of the previous pulse, it only tends to further saturate transformer 29 and therefore results in no output from the secondary windings. Note, the 10 or 15 hertz pole-changing rate of the signal on the line is relatively slow to the RC time constant of resistor 14 and capacitor 15A so that while the polarity on the line is in one state, capacitor 15A may charge and discharge through diac 27 a number of times before the line signal changes polarity but note, due to the square loop core characteristic of transformer 29, only the first pulse after the line has changed polarity resulting in an output from the transformer.

The second half of the 15 hertz detector circuitry 26 includes two one-shot multivibrators 90 and 91 and one AND gate 92. When the line starts its positive half-cycle, one-shot 90 is activated by a positive pulse through diode 93 providing a 41 millisecond gate pulse which is input via AND-gate 92 to one-shot 91. If the line changes to its negative polarity within the 41 millisecond gate of one-shot 90, a second pulse is transferred through transformer 29 and diode 94 and into AND- gate 92. Therefore, the input conditions to AND-gate 92 are satisfied and it will produce an output which will trigger the second one-shot 91 which will generate a 56 millisecond output pulse and energize relay 30. As long as the line pole changing signals are at 15 hertz, the AND-gate 92 is satisfied and the second one-shot 91 is triggered every cycle, producing a train of 56 millisecond pulses, thus holding up relay 30. The 41 millisecond duration of the gate of one-shot 90 is chosen to be just short of the cycle time of a 10 hertz signal and long enough to pick up the 15 hertz signal. The 10 hertz signal activates one-shot each 50 milliseconds therefore, when the gate of one-shot 91 is ready to be activated, no signal is present at the output of one-shot 90 for satisfying AND-gate 92. On the other hand, the input of one-shot 91 may be activated when 15 hertz signal is present because pulses appear every 33 milliseconds and within the gate of one-shot 90. That is, when one-shot 90 is delivering an output to AND-gate 92, a pulse appearing at the other input of gate 92 activates oneshot 91.

Assume now that the computer online repeater relay 23 has not been stepped for a period longer than the timeout cycle of timer 59, and a shift to 15 hertz has been accomplished at the control office. The input frequency thus activates the 15 hertz detector 26 and relay 30. 1f the 15 hertz is maintained for approximately one-half second, the timing circuitry 35 associated with contact 33 or relay 30 will not time out and the long shift relay 56 will remain deenergized. Once the 15 hertz signal is shifted back to 10 hertz, relay 30 is deenergized and capacitor 31 is discharged through back contacts 32, 37, and 38 of relays 30, 56 and 39 respectively to energize to an up or forward position the relay 40-40 and its associated contact 41 for energizing controller A. If the input signal of 15 hertz is maintained for longer than the timing cycle of timer 35, say in the order of 2 seconds, then relay 56 will be energized and when relay 30 is deenergized, front contact 37 will transmit the energy provided by charge capacitor 31 to back contact 42 of relay 43-43 for energizing its associated contact 44 up to energize to step control-B. This same sequence of events is used to cancel an activated state of either controller A or B. However, the sequence must be performed within the timeout cycle of timer 59 just after the computer online relay 17 has been deenergized for stepping of the controller. Under these circumstances, the relay 39-39 is energized to an up position and the contacts 38 and 42 will provide the energy transmitted from capacitor 31 and contact 37 to the down coils of relays 43-43 and 40-40 respectively. Depending upon how long a 15 hertz signal is applied to the line after the stepping of the controller, the long shift relay contact 37 will either be up or down for controlling the associated controller A or B.

What has been shown is a system for providing signals between the office and the field station over a communication channel by shifting the frequency of the input and having associated circuitry responsive to this change in frequency for controlling auxiliary devices in the field. By utilizing the condition of the stepping apparatus of the field devices, information for either activating or deactivating these devices may be taken advantage of without the necessity of increasing the number of line wires to the field station.

There has therefore been provided a vehicle traffic control system having a communication means including a single pair of line wires and remotely controlled apparatus for transmitting control signals to and from a local controller over the communication means, the controller is operable for providing signals for governing the control of vehicle traffic in accordance with the control signals and also operates to provide signals for controlling the vehicle traffic independently when remote control is terminated as when a malfunction occurs which blocks any control signals from the control apparatus to the local controller. There is an improvement in the system for providing remote control to at least two control devices coupled to a local controller which includes means at the control point for selectively designating a control frequency, an auxiliary means coupled to the local station control devices responsive to initiation of said control frequency for selectively energizing one or the other of said devices in accordance with the duration of the control frequency. There has also been provided a cancel control apparatus coupled to the local control devices responsive to the initiation of said control frequency, and an interrupt signal from the remote controllers operative for deenergizing one or the other of said control devices in accordance with the duration of the control frequency and reception of the interrupt at any time during a specific interval immediately preceding and following the initiation of said control frequency.

While there has been described what is considered to be the preferred embodiments, of the'invention, it will be obvious to those skilled in the. art that various changes and modifications may be made therein without departing from the invention and it is therefore aimed in the appended claims to cover all such changes the modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. A vehicle traffic control system having communication means including a pair of line wires, remotely located control apparatus for transmitting control signals to and receiving traffic information from a local controller over said communication means, said local controller operable to provide signals for controlling vehicle traffic in accordance with the control signals and also operable to provide signals for controlling the vehicle traffic independently when remote control is terminated wherein the improvement for communicating controls between the remotely located controller and at least two control devices coupled to said local controller comprises:

means at the control point for selectively designating a control frequency;

auxiliary means coupled to the local station control devices responsive to the initiation of said control signals for selectively energizing one or the other of said control devices in accordance with the duration of the control frequency; and

cancel control signal means coupled to the local control devices responsive to the initiation of said control frequency and an interrupt signal from said remote controllers operative for deenergizing one or the other of said control devices in accordance with the duration of the control frequency and reception of said interrupt any time during a specific time interval immediately preceding and following the initiation of said control frequency.

2. The apparatus of claim 1 wherein the auxiliary means further includes:

discriminating means responsive to a unique frequency of said control signals and blocking control signals of other than said unique frequency.

3. The apparatus of claim 2 wherein said discriminating means includes:

first gating means responsive to the control signal frequency, activated in accordance therewith for producing a first gate signal of predetermined duration;

second gating means having inputs responsive to the first gate signal and the control signal for producing a second gate signal when said first gate and control frequency signal are both present at its input; said second gate signal for activating said auxiliary means.

4. The apparatus of claim 3 wherein said first and second gating means are astable devices having gating intervals set at one of the anticipated control signal frequencies for discriminating that frequency as an operative control signal for activating the auxiliary means.

5. The apparatus of claim 4 wherein an input to said discriminating means includes a square loop transformer means situated at each polarity change of said control signals for providing a single pulse for activating said first and second gating means.

6. The apparatus of claim 5 wherein said input to the discriminating means includes a diac responsive to the control signals for providing a pulsed input to said square loop trans former in accordance with the control signal frequency.

7. The apparatus of claim 1 wherein the auxiliary means for selectively energizing one or the other of said local control devices includes:

a timer responsive to the initiation of said control frequency and producing signals relative to the duration thereof, and

a switching means responsive to the timer signals for selectively providing energy to one of thelocal control devices for ener'gization in accordance with said timer signals. 8. The apparatus of claim 7 wherein said control devices are magnetic stick relays adapted to maintain the response called for until specifically changed.

9. The apparatus of claim 1 including discriminator means at the control location discriminating transient noise signals from information and control signals.

10. The apparatus of claim 9 wherein the discriminator means comprises:

two relays connected in multiple each having a complementary conductance state with the other and stick circuits associated with each relay for sticking the other relay.

11. A vehicle traffic control system having a remote control apparatus for producing control signals and local apparatus coupled thereto for controlling traffic in accordance with said control signals wherein the improvement for controlling at least two local control devices includes:

a first relay energized in response to the reception of said control frequency;

first timing means responsive to the energized condition of said relay for producing a signal after a preset duration of said energized condition;

a charging circuit coupled to a front contact of said first relay;

a discharge path for said charging circuit coupled to one or the other of said local control devices via a back contact of said first relay;

a second relay energized in response to the first timing means signal when said first relay is in an energized condition for longer than said first time interval;

switching means governed by said second relay, coupled between said local control devices and said discharge path for selectively providing energy from said discharge path to one of the local control devices in accordance with the condition of said second relay;

a first polarized relay energized in response to momentary decoupling of the remote controller from the local controller;

second timing means responsive to the energized state of said polarized relay for deenergizing the polarized relay after a second time interval longer than said first interval;

second switching means governed by the polarized relay coupled between said first switching means and said local control device for selectively deenergizing one or the other of said local control devices in accordance with the condition of the second relay and the occurrence of a decoupling of said remote controller from said local controller within the first time interval.

* i IF 

1. A vehicle traffic control system having communication means including a pair of line wires, remotely located control apparatus for transmitting control signals to and receiving traffic information from a local controller over said communication means, said local controller operable to provide signals for controlling vehicle traffic in accordance with the control signals and also operable to provide signals for controlling the vehicle traffic independently when remote control is terminated wherein the improvement for communicating controls between the remotely located controller and at least two control devices coupled to said local controller comprises: means at the control point for selectively designating a control frequency; auxiliary means coupled to the local station control devices responsive to the initiation of said control signals for selectively energizing one or the other of said control devices in accordance with the duration of the control frequency; and cancel control signal means coupled to the local control devices responsive to the initiation of said control frequency and an interrupt signal from said remote controllers operative for deenergizing one or the other of said control devices in accordance with the duration of the control frequency and reception of said interrupt any time during a specific time interval immediately preceding and following the initiation of said control frequency.
 2. The apparatus of claim 1 wherein the auxiliary means further includes: discriminating means responsive to a unique frequency of said control signals and blocking control signals of other than said unique frequency.
 3. The apparatus of claim 2 wherein said discriminating means includes: first gating means responsive to the control signal frequency, activated in accordance therewith for producing a first gate signal of predetermined duration; second gating means having inputs responsive to the first gate signal and the control signal for producing a second gate signal when said first gate and control frequency signal are both present at its input; said second gate signal for activating said auxiliary means.
 4. The apparatus of claim 3 wherein said first and second gating means are astable devices having gating intervals set at one of the anticipated control signal frequencies for discriminating that frequency as an operative control signal for activating the auxiliary means.
 5. The apparatus of claim 4 wherein an input to said discriminating means includes a square loop transformer means situated at each polarity change of said control signals for providing a single pulse for activating said first and second gating means.
 6. The apparatus of claim 5 wherein said input to the discriminating means includes a diac responsive to the control signals for providing a pulsed input to said square loop transformer in accordance with the control signal frequencY.
 7. The apparatus of claim 1 wherein the auxiliary means for selectively energizing one or the other of said local control devices includes: a timer responsive to the initiation of said control frequency and producing signals relative to the duration thereof, and a switching means responsive to the timer signals for selectively providing energy to one of the local control devices for energization in accordance with said timer signals.
 8. The apparatus of claim 7 wherein said control devices are magnetic stick relays adapted to maintain the response called for until specifically changed.
 9. The apparatus of claim 1 including discriminator means at the control location discriminating transient noise signals from information and control signals.
 10. The apparatus of claim 9 wherein the discriminator means comprises: two relays connected in multiple each having a complementary conductance state with the other and stick circuits associated with each relay for sticking the other relay.
 11. A vehicle traffic control system having a remote control apparatus for producing control signals and local apparatus coupled thereto for controlling traffic in accordance with said control signals wherein the improvement for controlling at least two local control devices includes: a first relay energized in response to the reception of said control frequency; first timing means responsive to the energized condition of said relay for producing a signal after a preset duration of said energized condition; a charging circuit coupled to a front contact of said first relay; a discharge path for said charging circuit coupled to one or the other of said local control devices via a back contact of said first relay; a second relay energized in response to the first timing means signal when said first relay is in an energized condition for longer than said first time interval; switching means governed by said second relay, coupled between said local control devices and said discharge path for selectively providing energy from said discharge path to one of the local control devices in accordance with the condition of said second relay; a first polarized relay energized in response to momentary decoupling of the remote controller from the local controller; second timing means responsive to the energized state of said polarized relay for deenergizing the polarized relay after a second time interval longer than said first interval; second switching means governed by the polarized relay coupled between said first switching means and said local control device for selectively deenergizing one or the other of said local control devices in accordance with the condition of the second relay and the occurrence of a decoupling of said remote controller from said local controller within the first time interval. 